Various types of pressing detectors for detecting a pressing amount by the operator currently exist. For example, Patent Document 1 (identified below) discloses a conventional pressing detector that includes displacement sensor.
The displacement sensor of Patent Document 1 includes a piezoelectric element, a voltage conversion unit, and a detection unit. A voltage according to an amount of displacement is instantaneously generated from the piezoelectric element. The voltage conversion unit converts the voltage generated in the piezoelectric element into a voltage determined based on a pressing force and a predetermined time constant determined by an impedance of a resistor of the voltage conversion unit and capacitances of a capacitor and the piezoelectric element, and outputs the converted voltage. The detection unit integrates an output voltage of the voltage conversion unit and calculates an amount of pressing (pressing force) based on the integrated value.
However, when the displacement sensor uses the piezoelectric element here, an error also accumulates due to integration after the lapse of a certain time. As a result, the displacement sensor may erroneously detect that the operator is performing pressing although the operator is not actually performing pressing.
Therefore, in the displacement sensor described in Patent Document 1, after the integrated value of the voltage output from the voltage conversion unit becomes the maximum value, if a difference value obtained by differentiating between the initial integrated value and the latest integrated value is less than a predetermined threshold corresponding to the maximum value of the integrated value, the integrated value is corrected to the initial value.
Patent Document 1: International Publication No. WO 2013/111841.
As further described in Patent Document 1, the displacement sensor corrects the integrated value at the point in time when the integrated value of the voltage output from the voltage conversion unit becomes the maximum value. Thus, for example, when the operator releases the pressing before the integrated value becomes the maximum value, the integrated value is not reset to the initial value even if the difference value falls below the predetermined threshold value.
Therefore, the displacement sensor of Patent Document 1 has a problem of erroneously detecting that the operator is performing pressing, although the operator is not actually performing pressing.